Due to the ongoing development in an image quality of PDPs (Plasma Display Panel) that display an image using gas discharge, full HD (High Definition) panels which are capable of displaying hi-vision (high-definition) broadcasts while maintaining the original quality have been becoming popular. The full HD panels have discharge cells having an extremely smaller size than conventional panels. For example, a 42 inch visual size full HD panel has 1920×1080 discharge cells with a cell pitch of approximately 150 μm. A super hi-vision (ultra-high-definition) panel which is now being planned has approximately 8000×4000 discharge cells in the same visual panel size. An ultra-high-definition panel with a visual size of 100 inches has very small discharge cells with a cell pitch of approximately 100 μm.
In the high-definition and ultra-high-definition PDPs, a cell pitch is made significantly smaller than conventional PDPs. However, the problem with the small cells is that they tend to increase the discharge voltage, thereby decreasing the luminous efficiency.
To solve this problem, a conventional technique increased the luminous efficiency by increasing the ratio of the partial pressure of Xe in a Ne—Xe-based mixture gas, that is to say, a discharge gas, from conventional 10% or so to approximately 30%. However, using a lot of a Xe gas in the high-definition and ultra-high-definition PDPs adopting an MgO layer as the protective layer increases the discharge pressure. With the increased discharge pressure, sputtering amount of the protective layer increases, whereby the product life of the PDP is shortened. Further, due to the increase in the discharge voltage, the luminous efficiency cannot be greatly improved. The increase in the drive voltage also brings about another problem, namely, an increase in cost of the driver.
Also, the high-definition and ultra-high-definition PDPs have a larger surface area for barrier ribs than conventional PDPs, while they do not have a larger panel space for the protective layer. As a result, the phosphor coated area is increased by two to four times compared with the conventional PDPs. It is known that an impurity gas is released from a phosphor layer into the discharge gas over time. Besides, there is a possibility that organic components included in the binder, solvent, or the like which are attributed to a sealing material used in PDPs float in the discharge gas. The problem of such an impurity gas in the PDPs is that it prevents Xe from being excited, leading to an increase in the discharge voltage. If the impurity gas is absorbed by the protective layer, the secondary electron emission characteristics of the protective layer are also degraded. These effects also result in a decrease in luminous efficiency.
One method that has been recently proposed to solve the problem is to use the protective layer for the dielectric mainly composed of a high γ oxide, such as SrO, CaO, and BaO, as disclosed in Patent Literatures 1 and 2, and Non-Patent Literature 1. According to the literatures, since the high γ oxides are more reactive to impurity gases, such as CO, CO2 and, in particular, water vapor, than MgO, the discharge space is evacuated to a high vacuum of 1.0×10−4 Pa or less before the discharge gas is introduced in order to remove the impurity gas from the discharge space. The literatures also disclose that steps through a protective layer formation step to a sealing step are performed throughout in a dry atmosphere of air, N2, and O2, thereby preventing the protective layer from reacting with water vapor.
Further, Patent Literature 3 discloses a manufacturing method for PDPs including a protective layer composed of SrO, CaO, and BaO. According to the method, sealing and evacuating steps are performed throughout in a vacuum. The method was conceived in an attempt to prevent the protective layer from reacting with water vapor, CO, and CO2 in the air, while also promoting efficient evacuation of the impurity gas within the panel.
Moreover, Patent Literature 4 discloses a method for reducing discharge voltage by disposing a given absorbent material (i.e. ZSM-5-type zeolite ion-exchanged with copper ion) on the surface of a back panel that faces the discharge space within a PDP and causing the absorbent material to absorb an impurity gas to purify the discharge gas.
Moreover, Patent Literature 5 discloses a technique for disposing ion-exchanged zeolite either in a sealing member for a panel or in vicinity of the inner surface of the sealing member.